package com.cfwx.util.encryption;

/**
* A Base64 encoder/decoder.
* This class is used to encode and decode data in Base64 format as described in
* RFC 1521.
* 电子邮件传输算法
*/
public class Base64Coder {

 // The line separator string of the operating system.
 private static final String systemLineSeparator = System.getProperty("line.separator");

 // Mapping table from 6-bit nibbles to Base64 characters.
 private static char[] map1 = new char[64];
 static {
     int i = 0;
     for (char c = 'A'; c <= 'Z'; c++)
         map1[i++] = c;
     for (char c = 'a'; c <= 'z'; c++)
         map1[i++] = c;
     for (char c = '0'; c <= '9'; c++)
         map1[i++] = c;
     map1[i++] = '+';
     map1[i++] = '/';
 }

 // Mapping table from Base64 characters to 6-bit nibbles.
 private static byte[] map2 = new byte[128];
 static {
     for (int i = 0; i < map2.length; i++)
         map2[i] = -1;
     for (int i = 0; i < 64; i++)
         map2[map1[i]] = (byte) i;
 }

 /**
  * Encodes a string into Base64 format. No blanks or line breaks are
  * inserted.
  * 
  * @param s
  *            A String to be encoded.
  * @return A String containing the Base64 encoded data.
  */
 public static String encodeString(String s) {
     return new String(encode(s.getBytes()));
 }

 /**
  * Encodes a byte array into Base 64 format and breaks the output into lines
  * of 76 characters. This method is compatible with
  * <code>sun.misc.BASE64Encoder.encodeBuffer(byte[])</code>.
  * 
  * @param in
  *            An array containing the data bytes to be encoded.
  * @return A String containing the Base64 encoded data, broken into lines.
  */
 public static String encodeLines(byte[] in) {
     return encodeLines(in, 0, in.length, 76, systemLineSeparator);
 }

 /**
  * Encodes a byte array into Base 64 format and breaks the output into
  * lines.
  * 
  * @param in
  *            An array containing the data bytes to be encoded.
  * @param iOff
  *            Offset of the first byte in <code>in</code> to be processed.
  * @param iLen
  *            Number of bytes to be processed in <code>in</code>, starting
  *            at <code>iOff</code>.
  * @param lineLen
  *            Line length for the output data. Should be a multiple of 4.
  * @param lineSeparator
  *            The line separator to be used to separate the output lines.
  * @return A String containing the Base64 encoded data, broken into lines.
  */
 public static String encodeLines(byte[] in, int iOff, int iLen, int lineLen,
         String lineSeparator) {
     int blockLen = (lineLen * 3) / 4;
     if (blockLen <= 0)
         throw new IllegalArgumentException();
     int lines = (iLen + blockLen - 1) / blockLen;
     int bufLen = ((iLen + 2) / 3) * 4 + lines * lineSeparator.length();
     StringBuilder buf = new StringBuilder(bufLen);
     int ip = 0;
     while (ip < iLen) {
         int l = Math.min(iLen - ip, blockLen);
         buf.append(encode(in, iOff + ip, l));
         buf.append(lineSeparator);
         ip += l;
     }
     return buf.toString();
 }

 /**
  * Encodes a byte array into Base64 format. No blanks or line breaks are
  * inserted in the output.
  * 
  * @param in
  *            An array containing the data bytes to be encoded.
  * @return A character array containing the Base64 encoded data.
  */
 public static char[] encode(byte[] in) {
     return encode(in, 0, in.length);
 }

 /**
  * Encodes a byte array into Base64 format. No blanks or line breaks are
  * inserted in the output.
  * 
  * @param in
  *            An array containing the data bytes to be encoded.
  * @param iLen
  *            Number of bytes to process in <code>in</code>.
  * @return A character array containing the Base64 encoded data.
  */
 public static char[] encode(byte[] in, int iLen) {
     return encode(in, 0, iLen);
 }

 /**
  * Encodes a byte array into Base64 format. No blanks or line breaks are
  * inserted in the output.
  * 
  * @param in
  *            An array containing the data bytes to be encoded.
  * @param iOff
  *            Offset of the first byte in <code>in</code> to be processed.
  * @param iLen
  *            Number of bytes to process in <code>in</code>, starting at
  *            <code>iOff</code>.
  * @return A character array containing the Base64 encoded data.
  */
 public static char[] encode(byte[] in, int iOff, int iLen) {
     int oDataLen = (iLen * 4 + 2) / 3; // output length without padding
     int oLen = ((iLen + 2) / 3) * 4; // output length including padding
     char[] out = new char[oLen];
     int ip = iOff;
     int iEnd = iOff + iLen;
     int op = 0;
     while (ip < iEnd) {
         int i0 = in[ip++] & 0xff;
         int i1 = ip < iEnd ? in[ip++] & 0xff : 0;
         int i2 = ip < iEnd ? in[ip++] & 0xff : 0;
         int o0 = i0 >>> 2;
         int o1 = ((i0 & 3) << 4) | (i1 >>> 4);
         int o2 = ((i1 & 0xf) << 2) | (i2 >>> 6);
         int o3 = i2 & 0x3F;
         out[op++] = map1[o0];
         out[op++] = map1[o1];
         out[op] = op < oDataLen ? map1[o2] : '=';
         op++;
         out[op] = op < oDataLen ? map1[o3] : '=';
         op++;
     }
     return out;
 }

 /**
  * Decodes a string from Base64 format. No blanks or line breaks are allowed
  * within the Base64 encoded input data.
  * 
  * @param s
  *            A Base64 String to be decoded.
  * @return A String containing the decoded data.
  * @throws IllegalArgumentException
  *             If the input is not valid Base64 encoded data.
  */
 public static String decodeString(String s) {
     return new String(decode(s));
 }

 /**
  * Decodes a byte array from Base64 format and ignores line separators, tabs
  * and blanks. CR, LF, Tab and Space characters are ignored in the input
  * data. This method is compatible with
  * <code>sun.misc.BASE64Decoder.decodeBuffer(String)</code>.
  * 
  * @param s
  *            A Base64 String to be decoded.
  * @return An array containing the decoded data bytes.
  * @throws IllegalArgumentException
  *             If the input is not valid Base64 encoded data.
  */
 public static byte[] decodeLines(String s) {
     char[] buf = new char[s.length()];
     int p = 0;
     for (int ip = 0; ip < s.length(); ip++) {
         char c = s.charAt(ip);
         if (c != ' ' && c != '\r' && c != '\n' && c != '\t')
             buf[p++] = c;
     }
     return decode(buf, 0, p);
 }

 /**
  * Decodes a byte array from Base64 format. No blanks or line breaks are
  * allowed within the Base64 encoded input data.
  * 
  * @param s
  *            A Base64 String to be decoded.
  * @return An array containing the decoded data bytes.
  * @throws IllegalArgumentException
  *             If the input is not valid Base64 encoded data.
  */
 public static byte[] decode(String s) {
     return decode(s.toCharArray());
 }

 /**
  * Decodes a byte array from Base64 format. No blanks or line breaks are
  * allowed within the Base64 encoded input data.
  * 
  * @param in
  *            A character array containing the Base64 encoded data.
  * @return An array containing the decoded data bytes.
  * @throws IllegalArgumentException
  *             If the input is not valid Base64 encoded data.
  */
 public static byte[] decode(char[] in) {
     return decode(in, 0, in.length);
 }

 /**
  * Decodes a byte array from Base64 format. No blanks or line breaks are
  * allowed within the Base64 encoded input data.
  * 
  * @param in
  *            A character array containing the Base64 encoded data.
  * @param iOff
  *            Offset of the first character in <code>in</code> to be
  *            processed.
  * @param iLen
  *            Number of characters to process in <code>in</code>, starting
  *            at <code>iOff</code>.
  * @return An array containing the decoded data bytes.
  * @throws IllegalArgumentException
  *             If the input is not valid Base64 encoded data.
  */
 public static byte[] decode(char[] in, int iOff, int iLen) {
     if (iLen % 4 != 0)
         throw new IllegalArgumentException(
                 "Length of Base64 encoded input string is not a multiple of 4.");
     while (iLen > 0 && in[iOff + iLen - 1] == '=')
         iLen--;
     int oLen = (iLen * 3) / 4;
     byte[] out = new byte[oLen];
     int ip = iOff;
     int iEnd = iOff + iLen;
     int op = 0;
     while (ip < iEnd) {
         int i0 = in[ip++];
         int i1 = in[ip++];
         int i2 = ip < iEnd ? in[ip++] : 'A';
         int i3 = ip < iEnd ? in[ip++] : 'A';
         if (i0 > 127 || i1 > 127 || i2 > 127 || i3 > 127)
             throw new IllegalArgumentException("Illegal character in Base64 encoded data.");
         int b0 = map2[i0];
         int b1 = map2[i1];
         int b2 = map2[i2];
         int b3 = map2[i3];
         if (b0 < 0 || b1 < 0 || b2 < 0 || b3 < 0)
             throw new IllegalArgumentException("Illegal character in Base64 encoded data.");
         int o0 = (b0 << 2) | (b1 >>> 4);
         int o1 = ((b1 & 0xf) << 4) | (b2 >>> 2);
         int o2 = ((b2 & 3) << 6) | b3;
         out[op++] = (byte) o0;
         if (op < oLen)
             out[op++] = (byte) o1;
         if (op < oLen)
             out[op++] = (byte) o2;
     }
     return out;
 }

 // Dummy constructor.
 private Base64Coder() {
 }

} // end class Base64Coder

